Process for the manufacture of electrode pitches



PROCESS FOR THE MANUFACTURE OF ELECTRODE PITCHES Friedrich Croy, Schriesheim, Germany No Drawing. Application November 26, 1954 Serial No. 471,536

Claims. (Cl. 208-44) In the manufacture of electrodes for metallurgical purposes, a mixture of coke, graphite, anthracite or coal is compounded with coal-tar pitch as a binding agent and then baked. The coal-tar pitch forms in the baked electrode a coke skeleton which determines the stability and tensile strength of the finished electrode. That part of the coke which has the effect of increasing the electrodes strength is called binding coke, and the amount of binding coke forming during the baking operation depends to a large extent on the percentage of mediummolecular tar resins contained in the coal-tar pitch.

The coal-tar pitches produced according to known processes and available in commerce contain, as a rule, only from 13 to 17%, at best 23%, medium-molecular tar resins. Thus, the employment of these commercially available coal-tar pitches permits the formation of only a certain portion of binding coke in the finished electrodea portion which corresponds to the percentageof medium-molecular tar resins. In accordance with the present invention, the percentage of binding coke for the manufacture of electrodes is increased by providing a coal-tar pitch with a higher content of medium-molecular tar resins.

I have found that the content of medium-molecular tar resins in coal-tar pitch can be increased substantially beyond the aforementioned percentages through oxidizing polymerization or through polymerization and condensation, and the addition of certain chemical agents, so that a coal-tar pitch as heretofore unobtainable good quality is obtained which is particularly suitable for the manufacture of electrodes.

The new process comprises, generally, treating coal tar with a current of air, after adding not more than 5% of a heavy-metal chloride as a polymerization agent and a light tar oil, at temperatures of 150 to 200 0., followed by distillation to yield a pitch of the desired softening point. The process may also be started with a coal-tar pitch, in which case no distillation Will be necessary. Particularly advantageous is the employment of manganic, chromic, or ferric chloride in amounts of 1.5%. The new process yields a coal-tar pitch whose content of medium-molecular tar resins averages 30%.

It has also been found that the duration of the treatment can be substantially shortened, as compared with the employment of heavy-metal chlorides, without lowering the content of medium-molecular tar resins, if polymerization is effected in the presence of less than 5% of an organic sulfonic acid chloridesuch as paratoluenesulfonic acid chloride, nitrobenzene-sulfonic acid chloride, or nitronaphthalene sulfonic acid chloride. In this case it is also possible to substitute a mechanical stirring apparatus for stirring by means of an air current. When sulfonic acid chiorides are used, the duration of the treatment can be reduced to approximately minutes, while in the known process treatments of the prior art, several hours are required.

The new process yields coal-tar pitches whose content States Pate of medium-molecular tar resins amounts to as much as 32% so that they are particularly suitable as electrode pitches, since they make it possible to produce electrodes of exceptionally good stability and tensile strength.

Example I parts coal tar with 10 parts coal-tar oil (D 1.02- 1.03) and 0.2 part manganic chloride are treated with a current of air for 8 hours at C. Thereupon the mixture is distilled to yield a pitch with a softening point in the range of 65 to 75 C. (according to K. S. Analysis of the pitch gave the following values:

Softening point 72 C. (acc. to K. 8. coke 47.4%,

ashes 0.34%.

Percent Insoluble in benzene 42.0 High-molecular tar resins 11.7 Medium-molecular tar resins 30.3 Low-molecular tar resins 50.9

Oils m+n 7.1

Example II 70 parts coal-tar pitch with a softening point of 70 C. (acc. to K. S.), and 30 parts coal-tar oil (D 1.078) after adding 0.5% chromic chloride are treated with a current of air for 15 hours at C. Analysis of the reaction product shows:

Softening point 85.5 C. (acc; to K. S.), coke 36.4%,

ashes 0.32%.

Percent Insoluble in benzene 33.7 Higlnmolecular tar resins 4.4 Medium-molecular tar resins 29.3 Low-molecular tar resins 60.2 Oils m-I-n 6.1

Example III -100 parts coal-tar pitch with a softening point of 84 C. (acc. to K. S.), and 3 parts nitrobenzene-sulfonic acid chloride are stirred for ten minutes with a mechanical stirring apparatus (about 80 turns) at 160 to C. The reaction product gives the following analytical values:

Softening point 84 C. (acc. to K. S.), coke 54.0%,

ashes 0.22%.

Percent Insoluble in benzene 37.3

High-molecular tar resins 6.1

Medium-molecular tar resins 31.2

Low-molecular tar resins 58.3

Oils m+n 4.4

Example IV 100 parts coal-tar pitch with a softening point of 89 C. (acc. to K. S.), and 2.5 parts paratoluene-sulfonic acid chloride are stirred by means of an air current (distributor spider) for 10 minutes at a temperature of 172 C. The reaction product shows the following analytical values:

Softening point 93 C. (acc. to K. S.), coke 53.6%,

1. The process for preparing an electrode coal tar pitch composition containing at least 30% by weight of Krtimer Sarnow method of measuring inciting points.

medium-molecular weight tar resins Comprising mixing a coal tar with a light coal tar oil and a compound in an amount up to approximately 5% by weight of the mixture at a temperature of approximately 150 C. to approximately 200 C., said compound being selected from the group consisting of ,manganic chloride, chromic chloride, ferric chloride, nitrobenzene sulfonic acid chloride, paratoluene sulfonic acid chloride, and nitronaphthalene sulfonic acid chloride, stirring the so-formed mixture, and distilling the so-treated mixture until the residue has a softening point of approximately 80 C. Kramer-Sarnow, thereby obtaining a coal tar pitch for forming electrodes of exceptionally good stability and high tensile strength.

2. The process for preparing an electrode coal tar pitch composition containing at least 30% by weight of medium-molecular weight tar resins comprising mixing a coal tar with a light coal tar oil andup to approximately 5%, by weight of the mixture, of nitrobenzene sulfonic acid chloride at a temperature of approximately 150 C. to approximately 200 C., stirring the so-formed mixture and distilling the so-treated mixture until the residue has a softening point of approximately 80 C. Kramer- Sarnow, thereby obtaining a coal tar pitch for forming electrodes of exceptionally good stability and high tensile strength.

3. The process for preparing an electrode coal tar pitch composition containing at least 30% by weight of medium-molecular weight tar resins comprising mixing a coal tar with a light coal tar oil and up to approximately 5%, by weight of the mixture, of paratholuene sulfonic acid chloride at a temperature of approximately 150 C. to approximately 200 C., stirring the so-formed mixture and distilling the so-treated mixture until the residue has a softening point of approximately 80 C. Kramer- Sarnow, thereby obtaining a coal, tar pitch for forming 4 electrodes of exceptionally good stability and high tensile strength.

4. The process for preparing an electrode coal tar pitch composition containing at least 30% by weight of medium-molecular weight tar resins comprising mixing a coal tar with a light coal tar oil and up to approximately 5%, by weight of the mixture, of nitronaphthalene sulfonic acid chloride at a temperature of approximately 150 C. to approximately 200 C., stirring the so-formed mixture and distilling the so-treated mixture until the residue has a softening point of approximately C. Kramer-Sarnow, thereby obtaining a coal tar pitch for forming electrodes of exceptionally good stability and high tensile strength.

5. The process for preparing an electrode coal tar pitch composition containing at least 30% by weight of medium-molecular weight tar resins comprising mixing a coal tar with a light coal tar oil and up to approximately 5%, by weight of the mixture, of manganic chloride at a temperature of approximately C. to approximately 200 C., stirring the so-formed mixture and distilling the so-treated mixture until the residue has a softening point of approximately 80 C. Kramer- Sarnow, thereby obtaining a coal tar pitch for forming electrodes of exceptionally good stability and high tensile strength.

References Cited in the file of this patent UNITED STATES PATENTS 2,095,190 Heuscher Oct. 5, 1937 2,179,208 Burk et a1 Nov. 7, 1939 2,303,769 Stevens et al Dec. 1, 1942 2,478,654 Croyere Aug. 9, 1949 2,500,208 Shea et al. Mar. 14, 1950 2,683,197 Juel July 6, 1954 

1. THE PROCESS FOR PREPARING AN ELECTRODE COAL TAR PITCH COMPOSITION CONTAINING AT LEAST 30% BY WEIGHT OF MEDIUM-MOLECULAR WEIGHT TAR RESINS COMPRISING MIXING A COAL TAR WITH A LIGHT COAL TAR OIL AND A COMPOUND IN AN AMOUNT UP TO APPROXIMATELY 5% BY WEIGHT OF THE MIXTURE AT A TEMPERATURE OF APPROXIMATELY 150*C. TO APPROXIMATELY 200*C., SAID COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF MANGANIC CHLORIDE, CHROMIC CHLORIDE, FERRIC CHLORIDE, NITROBENZENE SULFONIC ACID CHLORIDE, PARATOLUENE SULFONIC ACID CHLORIDE, AND NITRONAPHTHALENE SULFONIC ACID CHLORIDE, STIRRING THE SO-FORMED MIXTURE, AND DISTILLING THE SO-TREATED MIXTURE UNTIL THE RESIDUE HAS A SOFTENING POINT OF APPROXIMATELY 80*C. KRAMER-SARNOW, THEREBY OBTAINING A COAL TAR PITCH FOR FORMING ELECTRODES OF EXCEPTIONALLY GOOD STABILITY AND HIGH TENSILE STRENGTH. 